Targeting Mitochondrial Redox Capacity to Overcome Cancer Subtype that Regrowth After Radiation

PROJECT SUMMARY
Radiation therapy (RT) is widely used to treat localized prostate cancer (PCa). However, cancer cells often
develop resistance to RT through unknown mechanisms, resulting in cancer recurrence. To improve RT, there
is a dire need to uncover cellular events that cause cells to become resistant. We previously demonstrated that
PCa heterogeneity, particularly in prostate cancers with an abundant mitochondria subpopulation, often survive
and regrow after RT (termed radiation resistant prostate cancer, or RR-PCa). Elevation of mitochondrial mass,
number, reactive oxygen species (ROS), and biogenesis markers is acquired in RR-PCa cells. We further
demonstrated that knockdown of the mitochondrial biogenesis regulator, TFAM (transcription factor A,
mitochondrial), significantly restored the sensitivity of RR-PCa cells to RT. Hence, our overarching hypothesis is
that RT-activated mitochondrial biogenesis, via ROS, is an acquisition mechanism that drives PCa survival post-
RT, a premise that will undergo stringent examination in the proposed studies. ROS are known to directly and
indirectly regulate mitochondrial homeostasis through fusion, fission, mitophagy, and biogenesis. We screened
FDA-approved drugs in search of compounds that are nontoxic to normal cells and have the ability to raise the
level of mitochondrial hydrogen peroxide (mtH2O2) in PCa cells while blocking mitochondrial protein translation.
We found azithromycin (AZM), a macrolide antibiotic, to be an effective prototype compound that possesses
both properties. We further demonstrated that AZM combined with RT enhances the death of PCa cells with an
abundant mitochondrial subpopulation, compared to AZM or RT alone. Thus, we propose to advance our findings
and identify the mechanism(s) that effectively inhibit the survival of post-irradiated cancer cells, to improve RT
efficacy. The specific aims are: 1) to define the molecular mechanism(s) by which RT-activated mitochondrial
biogenesis promotes cell survival and metabolic adaptations of PCa cells with abundant mitochondria, both in
vitro and in vivo; 2) to determine if overloading mtH2O2 to target inherent mitochondria and RT-acquired
mitochondria while blocking mitochondrial protein translation in RT-acquired mitochondria enhances
radiosensitivity of RR-PCa cells, and 3) to improve RT using a mtH2O2 generator and a mitochondrial protein
translation inhibitor, AZM as prototype, in an orthotopic mouse xenograft model and a patient-derived xenograft
model of PCa with activated mitochondrial biogenesis. This study uses state-of-the-art platforms including the
reverse phase protein array, stable isotope-resolved metabolomics, super-resolution microscopy with Imaris
software, TEMPOL-enhanced MRI imaging, and a high resolution O2k-FluoRespirometer. The proposed studies
are expected to uncover novel molecular insights by which concurrently targeting mitochondrial redox capacity
and mitochondrial biogenesis improve RT efficacy of RR-PCa.

Grant Number: 3R01CA251663-05S1
NIH Institute/Center: NIH
Principal Investigator: Luksana Chaiswing